1. Field of the Invention
The present invention relates to a chain tensioner for keeping the tension of a chain constant, which is placed on a loose side of the chain, in a chain transmission system for transmitting the rotation of a crank shaft to a cam shaft, for example, in a vehicle engine.
2. Description of the Related Art
As the above-described chain tensioner, a chain tensioner having the following structure is conventionally known. A spring and a plunger are housed within a housing so that outward projection ability is imparted to the plunger by an elastic force of the spring. In this chain tensioner, the plunger, which is elastically pressed by the spring, pushes the chain so as to bring the chain into a tensed state. On the other hand, the pushing force imparted to the plunger by the chain is buffered by an oil pressure in an oil hydraulic damper chamber formed in the rear of the plunger to keep a tensile force of the chain constant. As specific structures, for example, those described in, for example, Japanese Patent Laid-Open Publication Nos. 2001-146946 and 2001-355691 are known.
In this type of chain tensioner, a register ring is provided as a member for regulating the backward movement of the plunger (return regulation). The register ring is engaged with a first stopper formed on the inner circumferential surface of the housing while being fitted into any of a plurality of engagement grooves formed on the outer circumferential surface of the plunger. As described above, the register ring plays an important role in regulation of the backward movement of the plunger so as to prevent the chain from being excessively loosened and the like.
As described above, the register ring is an important component in view of realization of the functions of the chain tensioner. Therefore, the design conditions of the register ring such as a shape and a material should be deliberately determined in consideration of the functions of the chain tensioner.